Neopentyl glycol (hereinafter "NPG") is an important starting material for the preparation of various useful products such as lubricants, plastics, surface coatings and synthetic resins. NPG has commonly been produced by effecting an aldol condensation of isobutyraldehyde and formaldehyde, followed by the hydrogenation of the condensation product, hydroxypivaldehyde. One type of aldol catalyst used with these reactions has been an alkali metal-containing catalyst, such as sodium carbonate. However, these catalysts produce a condensation product containing a high amount of undesirable carboxylic acid salts, which must be removed prior to hydrogenation. Additionally, use of sodium-based aldol catalysts can jeopardize the effectiveness of a hydrogenation catalyst such as Raney nickel. The successful use of the Raney nickel hydrogenation catalyst requires the removal of the sodium prior to hydrogenation in order to prevent deactivation of the catalyst, or decomposition of the hydroxypivaldehyde to formaldehyde, which will poison the nickel catalyst.
Other catalysts useful in producing the aldol condensation product of isobutyraldehyde and formaldehyde are tertiary amines, such as those described in U.S. Pat. No. 3,808,280. Although the use of tertiary amines has provided high yields of the desired hydroxypivaldehyde, with low levels of by-products such as isobutyraldoxane and NPG isobutyrate, there by-products must be stripped from the hydroxypivaldehyde before hydrogenation to the NPG product, because they form impurities upon hydrogenation, such as 2,2,4-trimethyl-1,3-pentanediol (TMPD) and isobutanol, which are very difficult to remove from the ultimate NPG product. Additionally, the hydrogenation of hydroxypivaldehyde crude product produced by the aldol condensation reaction must be carried out at high pressures, e.g., 4,000 psig, or excessive by-product formation results. This by-product formation occurs largely because residual tertiary amine catalyst is present in the hydroxypivaldehyde crude product, and tends to cause decomposition thereof during the hydrogenation, producing decomposition products that lower total NPG production and increase unwanted impurities, such as isobutanol. Simultaneously, the residual tertiary amine catalyst and decomposition products tend to rapidly deactivate or poison the hydrogenation catalyst. Heretofore, in order to avoid this high by-product formation it has been necessary to remove the residual catalyst and decomposition products prior to the hydrogenation, or conduct the hydrogenation under high pressures.
It is thus desirable to have a process which can maximize yield of NPG and minimize formation of unwanted impurities. It is further desirable to perform this production with a minimum of steps, and without the need to conduct the reaction at high pressures.